base.rb

require 'daru/io/base'

module Daru
  module IO
    module Exporters
      # Base Exporter Class that contains generic helper methods, to be
      # used by other Exporters via inheritence
      class Base < Daru::IO::Base
        # Checks whether the first argument given to any `Daru::IO::<Exporter>` module
        # is a `Daru::DataFrame`. Raises an error when it's not a `Daru::DataFrame`.
        #
        # @param dataframe [Daru::DataFrame] A DataFrame to initialize
        #
        # @example Stores the dataframe
        #   df = Daru::DataFrame.new([[1,2],[3,4]], order: [:a, :b])
        #   Daru::IO::Exporters::Base.new(df)
        #
        #   #=> #<Daru::IO::Exporters::Base:0x007f899081af08 @dataframe=#<Daru::DataFrame(2x2)>
        #   #      a   b
        #   #  0   1   3
        #   #  1   2   4>
        #
        # @example Raises error when not a DataFrame
        #   Daru::IO::Exporters::Base.new(nil)
        #
        #   #=> ArgumentError: Expected first argument to be a Daru::DataFrame, received NilClass instead
        def initialize(dataframe)
          unless dataframe.is_a?(Daru::DataFrame)
            raise ArgumentError,
              'Expected first argument to be a Daru::DataFrame, '\
              "received #{dataframe.class} instead."
          end
          @dataframe = dataframe
        end

        # Exports an Exporter instance to a file-writable String.
        #
        # @return A file-writable `String`
        #
        # @example Getting a file-writable string from Avro Exporter instance
        #
        #   instance = Daru::IO::Exporters::Format.new(opts)
        #   instance.to_s #! same as df.to_format_string(opts)
        def to_s(file_extension: '')
          tempfile = Tempfile.new(['filename', file_extension])
          path     = tempfile.path
          write(path)

          File.read(path)
        end
      end
    end
  end
end